Conventionally, semiconductor memories have been used widely for a random access memory (RAM) represented by DRAM, SRAM and the like. High integration due to improvements in fine-processing techniques and cost reduction due to improvements in the volume-production techniques have been pursued, and thus semiconductor memories have been used widely for memories in various products and devices. Though such a semiconductor memory like a DRAM has excellent volume-productivity, it may have problems in some characteristics such as the repeatability in recording and heat resistance. For example, since an ordinary DRAM is supposed to be used at a temperature not higher than 100° C., when the environmental temperature exceeds the range and becomes even higher, the characteristics as a memory can deteriorate.
Among the semiconductor memories, semiconductor memories represented by Flash Memory (trade name) have been used widely for various devices because of a trend of integration and high capacity due to the improvements in the fine process techniques and the trend of cost reduction due to the improvements in the volume-production techniques. The Flash Memory is roughly classified into a NAND type and a NOR type. However, an ordinary Flash Memory has a problem in the speed of recording and reading information. In addition, the Flash Memory has the following problems that, for example, it requires a batched cancellation before information recording, it consumes a large amount of power, and it is affected easily by external environments such as radioactive rays and stress.
Recently, a magnetic memory (MRAM) as a RAM using a Magneto-Resistive Element (MR element) has been developed. The MRAM has an excellent repetitive recording characteristic, and it also has some excellent characteristics, for example, it can read and record at high speed in comparison with Flash Memory or the like, and thus it has been developed keenly for the next-generation memory. Such a MRAM is disclosed, for example, in JP2002-533916A. However, since the MRAM changes its characteristics greatly depending on the thickness of its thin film composing the MR elements, the film thickness must be controlled on the order of nanometers in the manufacturing process. The MR elements are classified in accordance with the type of the nonmagnetic layers included into a GMR element (Giant Magneto-Resistive Element) and a TMR element (Tunneling Magneto-Resistive Element). For example, in the TMR element, an Al2O3 layer that is generally used for a nonmagnetic layer has a thickness in a range of sub-nanometers to several nanometers. It is difficult to control the variation in the film thickness on the sub-nanometer order in a manufacturing process. Therefore, for example, in a case of forming plural MR elements on a substrate such as a silicon (Si) wafer, it is difficult to control characteristics among elements within a predetermined range, and this imposes problems in the volume productivity and integration by fine processing.
Another example of RAM being in use at present or under development is a ferromagnetic memory that uses a dielectric polarization phenomenon of a ferromagnetic material. However, the ferromagnetic memory has some problems. For example, the characteristics deteriorate in manufacturing due to contamination with a slight amount of hydrogen or the like, it is not suitable for fine processing, applicable temperature ranges are limited, and it is easily affected by stress or the like. A phase-change memory that uses a phase transition phenomenon of materials is under development as well. However, since such a memory uses a phenomenon of phase transition between amorphous and crystal, it has some problems, for example, its non-volatile property deteriorates under a high-temperature environment, and stress and distortion that may occur as a result of a volume change at the time of phase change are difficult to suppress.